In large reasealable food storage plastic bag, mix dressing and 1 teaspoon Italian seasoning.
Add chicken; turn to coat with marinade. Seal bag and refrigerate, turning chicken occasionally, at least 1 hour but no longer than 24 hours.
Heat coals or gas grill for direct heat. Remove chicken from marinade; reserve marinade. Place chicken on grill over medium heat. Cover grill; cook 10 to 12 minutes, turning halfway through grilling and brushing with marinade from plastic bag, until juice is clear when center of thickest part is cut (165°F).
In medium bowl, stir together tomatoes, olive oil, 1/2 teaspoon Italian seasoning, salt and pepper. Serve chicken topped with fresh tomato salsa.